feat(scripts): add dogfood-build.sh — build from checkout and verify provenance

Builds claw from the current HEAD, then checks that the binary's
git_sha matches git rev-parse --short HEAD. Exits non-zero if the
binary is stale or provenance is opaque (git_sha: null).

Usage:
  CLAW=$(bash scripts/dogfood-build.sh)   # fail-fast if stale
  $CLAW version --output-format json       # provenance confirmed

Addresses ROADMAP #69: dogfooders using a stale installed binary
cannot attribute behavior to specific commits. This script makes
dogfood round zero unambiguous.

Also documents the safe workaround for contributors who have a
stale system-installed binary.

scripts/dogfood-build.sh

@@ -0,0 +1,38 @@
+#!/usr/bin/env bash
+# dogfood-build.sh — Build claw from current checkout and verify provenance.
+# Usage: bash scripts/dogfood-build.sh
+# On success: prints the verified binary path. Use as:
+#   CLAW=$(bash scripts/dogfood-build.sh) && $CLAW version --output-format json
+set -euo pipefail
+
+REPO_ROOT="$(cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd)"
+RUST_DIR="$REPO_ROOT/rust"
+BINARY="$RUST_DIR/target/debug/claw"
+EXPECTED_SHA="$(git -C "$REPO_ROOT" rev-parse --short HEAD)"
+
+echo "▶ Building claw from $REPO_ROOT ($(git -C "$REPO_ROOT" log --oneline -1))..." >&2
+cargo build --manifest-path "$RUST_DIR/Cargo.toml" -p rusty-claude-cli -q
+
+if [[ ! -x "$BINARY" ]]; then
+    echo "✗ Build succeeded but binary not found at $BINARY" >&2
+    exit 1
+fi
+
+BINARY_SHA=$("$BINARY" version --output-format json 2>/dev/null \
+    | python3 -c "import sys,json; d=json.load(sys.stdin); print(d.get('git_sha','null'))" 2>/dev/null || echo "null")
+
+if [[ "$BINARY_SHA" == "null" || -z "$BINARY_SHA" ]]; then
+    echo "✗ Provenance check failed: binary reports git_sha: null" >&2
+    echo "  Binary: $BINARY" >&2
+    exit 1
+fi
+
+if [[ "$BINARY_SHA" != "$EXPECTED_SHA" ]]; then
+    echo "✗ Provenance mismatch: binary=$BINARY_SHA, HEAD=$EXPECTED_SHA" >&2
+    echo "  Rerun after 'git pull' or check for uncommitted changes." >&2
+    exit 1
+fi
+
+echo "✓ Binary verified: $BINARY_SHA == HEAD ($EXPECTED_SHA)" >&2
+echo "  To dogfood: export CLAW=$BINARY" >&2
+echo "$BINARY"